1. Field of the Invention
The present invention relates to a mobile communication system, a mobile terminal and a transmission diversity application method used therefor, and in particular, to a system for applying closed-loop type transmission diversity to both a PDSCH (Physical Downlink Shared Channel) and a DPCH (Dedicated Physical Channel).
2. Description of the Prior Art
In recent years, mobile terminals (mobile stations) such as portable telephones are increasingly rendered multimedia-capable for the purpose of handling a large-capacity static image, short-time animation and so on so that a large-capacity and high-speed data transmission method is required along with it.
As for this large-capacity and high-speed data transmission method, a PDSCH method, an HS-PDSCH (High Speed-Physical Downlink Shared Channel) method and so on wherein only a downward (a direction from a base station to a mobile station) transmission speed is accelerated are proposed.
As for a system using the PDSCH method, there is a system wherein a DPCH is sent from the base station to a large number of mobile stations in a standby status waiting for reception of PDSCH data, and the PDSCH and DPCH are sent from the base station to the mobile station just receiving the PDSCH data.
In the case of applying closed-loop type transmission diversity to both the PDSCH and DPCH in this system, the mobile station determines a transmission diversity control information on the DPCH based on receiving quality of a CPICH (Common Pilot Channel) or the DPCH after diversity synthesis, and determines the transmission diversity control information on the PDSCH based on the receiving quality of the CPICH or the DPCH of the base station sending the PDSCH. After that, the mobile station notifies the base station of both the transmission diversity control information on the DPCH and transmission diversity control information on the PDSCH.
Moreover, when switching of the base station to another base station is performed by soft handover in the case where the mobile station moves from a cell in a control range of a certain base station to the cell of another base station in this system, the control information to be fed back to the base station for the transmission diversity is different between the PDSCH and the DPCH.
Here, operation of the transmission diversity is shown FIG. 12. In the case of performing this transmission diversity, CPICHs #11, #12, the DPCH and the PDSCH are synthesized in synthesis portions 41 and 42 of a base station 4 respectively and sent to a mobile station 3 from antennas 43 and 44.
The mobile station 3 detects a phase difference of the CPICHs #11 and #12 and feeds back information on the phase difference thereof to the base station 4 as the transmission diversity control information. The base station 4 controls the transmission based on the control information that is fed back so that a receiving state at said mobile station 3 becomes the best.
As for the above-mentioned system of the past using the PDSCH method, it requires different control information between the PDSCH and the DPCH during the soft handover in the case of applying closed-loop type transmission diversity to both the PDSCH and DPCH, and so the respective control information on the PDSCH and the DPCH is fed back to the base station, resulting in an increased number of bits of the control information to the base station.
In addition, as the respective control information on the PDSCH and the DPCH is separately sent to the base station if the number of bits of the control information to the base station is fixed, it is necessary to render a feedback period longer, so that characteristics in a relatively high-speed fading environment deteriorate and circuit capacity decreases.